Mucosal IL-12 is more effective than systemic IL-12 in augmenting IFN-gamma expression and inhibiting allergic lung eosinophilia in murine lungs

Allergen challenge induces Ifng dependent GTPases in the lungs as part of a Th1 transcriptome response in a murine model of allergic asthma

According to the current paradigm, allergic airway inflammation is mediated by Th2 cytokines and pro-inflammatory chemokines. Since allergic inflammation is self-limited, we hypothesized that allergen challenge simultaneously induces anti-inflammatory genes to counter-balance the effects of Th2 cytokines and chemokines. To identify these putative anti-inflammatory genes, we compared the gene expression profile in the lungs of ragweed-sensitized mice four hours after challenge with either PBS or ragweed extract (RWE) using a micro-array platform. Consistent with our hypothesis, RWE challenge concurrently upregulated Th1-associated early target genes of the Il12/Stat4 pathway, such as p47 and p65 GTPases (Iigp, Tgtp and Gbp1), Socs1, Cxcl9, Cxcl10 and Gadd45g with the Th2 genes Il4, Il5, Ccl2 and Ccl7. These Th1-associated genes remain upregulated longer than the Th2 genes. Augmentation of the local Th1 milieu by administration of Il12 or CpG prior to RWE challenge further upregulated these Th1 genes. Abolition of the Th1 response by disrupting the Ifng gene increased allergic airway inflammation and abrogated RWE challenge-induced upregulation of GTPases, Cxcl9, Cxcl10 and Socs1, but not Gadd45g. Our data demonstrate that allergen challenge induces two sets of Th1-associated genes in the lungs: 1) Ifng-dependent genes such as p47 and p65 GTPases, Socs1, Cxcl9 and Cxcl10 and 2) Ifng-independent Th1-inducing genes like Gadd45g. We propose that allergen-induced airway inflammation is regulated by simultaneous upregulation of Th1 and Th2 genes, and that persistent unopposed upregulation of Th1 genes resolves allergic inflammation.

Targeting memory Th2 cells for the treatment of allergic asthma

Th2 memory cells play an important role in the pathogenesis of allergic asthma. Evidence from patients and experimental models indicates that memory Th2 cells reside in the lungs during disease remission and, upon allergen exposure, become activated effectors involved in disease exacerbation. The inhibition of memory Th2 cells or their effector functions in allergic asthma influence disease progression, suggesting their importance as therapeutic targets. They are allergen specific and can potentially be suppressed or eliminated using this specificity. They have distinct activation, differentiation, cell surface phenotype, migration capacity, and effector functions that can be targeted singularly or in combination. Furthermore, memory Th2 cells residing in the lungs can be treated locally. Capitalizing on these unique attributes is important for drug development for allergic asthma. The aim of this review is to present an overview of therapeutic strategies targeting Th2 memory cells in allergic asthma, emphasizing Th2 generation, differentiation, activation, migration, effector function, and survival.

Interleukin-12: potential role in asthma therapy

Asthma is an inflammatory disease of the airways leading to significant morbidity and mortality. With advances in the understanding of the molecular and cellular mechanisms involved in the asthmatic response, researchers have identified specific mediators that may be targeted to control the inflammatory state of asthma. The Th2 hypothesis proposes that the inflammation in asthma arises from an imbalance between the two CD4+ T lymphocyte subsets, T helper (Th) type 1 and Th2. Th2 cells release many cytokines that have been shown to regulate the inflammatory response, while the Th1 cytokines counteract this response. The Th1 cytokine, interleukin (IL)-12, has been a target of intense study because it mediates the Th1 response and offers a means of modifying the asthmatic inflammatory response. Numerous murine studies have shown that this cytokine can potently inhibit allergic airway inflammation in asthma. Inhalation of IL-12 has been shown to increase its efficacy in inhibiting allergic inflammation in murine models while decreasing adverse effects seen with systemic administration of this cytokine. However, an initial study of inhaled IL-12 in humans with asthma was terminated because of adverse effects. The use of systemically administered IL-12 in patients with asthma has been limited due to cytokine toxicity. Another treatment option that has the potential of inducing a Th1 cytokine response is the use of IL-12 linked to polyethylene glycol (PEG) moieties. This mode of administration is likely to enhance cytokine delivery to the target organ, while decreasing its toxicity. IL-12 gene therapy has also been examined as a means of suppressing airway hyperreactivity in murine asthma, but its potential in human asthma has not been explored. Several recent studies have investigated the role of CpG DNA motifs as endogenous inducers of IL-12 with encouraging results in both mice and humans. These studies may result in novel Th1- inducing CpG-based immunotherapies for asthma.

In vivo role of p38 mitogen-activated protein kinase in mediating the anti-inflammatory effects of CpG oligodeoxynucleotide in murine asthma

DNA containing unmethylated CpG motifs is intrinsically immunostimulatory, inducing the production of a variety of cytokines and chemokines by immune cells. The strong Th1 response triggered by CpG oligodeoxynucleotide (ODN) inhibits the development of Th2-mediated allergic asthma in mice. This work documents that CpG ODN-induced IL-12 production plays a critical role in this process, because intrapulmonary CpG ODN inhibits allergic inflammation in wild-type but not IL-12(-/-) mice. CpG ODN rapidly localized to alveolar macrophages (AM), thereby triggering the phosphorylation of p38 mitogen-activated protein kinase (MAP kinase). AM cultured with CpG but not control ODN up-regulated IL-12 p40 expression and release, and these effects were blocked by the highly specific p38 MAP kinase inhibitor SB202190. Intrapulmonary administration of this inhibitor blocked the ability of CpG ODN to produce IL-12 in the lungs and reversed the anti-inflammatory effects of CpG ODN on allergic lung inflammation. These findings indicate that IL-12 production by AM is stimulated by intrapulmonary CpG ODN administration through a p38 MAP kinase-dependent process, and IL-12 is a key cytokine that mediates CpG ODN-induced protection against allergic lung inflammation.

Asthma: future directions

Asthma continues to be a significant health care problem, as reflected by the increasing rise in disease morbidity and mortality. Because steroids are relatively safe, clinically effective, and easy to administer, they remain the gold standard of treatment. After many decades of use, however, it is apparent that inhaled corticosteroids have failed to halt the progression of the asthma epidemic. Newer, more effective drugs are being developed to combat this disease, and the interest in developing new medications to treat allergic disease and asthma has increased exponentially. The financial burden of asthma has also been a significant motivating factor in the development of new medications. It is estimated that in 1998 the total cost of asthma on society was $11 billion [175]. This consideration has further intensified the quest to develop more effective asthma medications. Table 1 reviews the wide array of drugs currently being investigated. With the development and approval of novel asthma treatments, millions of asthma sufferers will undoubtedly have increased therapeutic options for control of their disease in the near future.

Interleukin-12 inhibits eosinophil differentiation from bone marrow stem cells in an interferon-gamma-dependent manner in a mouse model of asthma

BACKGROUND

Intrapulmonary administration of IL-12 has been shown to inhibit the number of eosinophils in lung murine models of asthma, but the precise mechanism of this inhibition has not been reported. The purpose of this study was to examine whether IL-12 treatment inhibits bone marrow eosinophilopoiesis, and to elucidate the role of IFN-gamma in this process.

OBJECTIVE

To elucidate the in vivo and in vitro effects of IL-12 on eosinophil differentiation from murine bone marrow (BM) stem cells, and to examine the mechanistic role of IFN-gamma in this process.

METHODS

Allergen-sensitized BALB/c mice were administered low doses of intranasal IL-12 at the time of allergen challenge, and the number of eosinophils in BM was determined 3 days later. The direct actions of IL-12 on eosinophil differentiation from BM cells were determined in vitro. The mechanistic role of IFN-gamma was assessed by measuring IFN-gamma induction by IL-12 in BM cell cultures, and through the use of IFN-gamma KO mice.

RESULTS

Treatment of allergic mice with intrapulmonary IL-12 (1 ng or 10 ng) reduced eosinophils in BM by 43%. Culture of BM cells from allergen-sensitized mice with IL-3 + IL-5 induced eosinophil differentiation in vitro. Addition of IL-12 to these cultures inhibited eosinophil differentiation, with maximal inhibition (45%) occurring at 10 ng/mL IL-12 concentration. IL-12 induced IFN-gamma production from BM cultures, and failed to inhibit eosinophil differentiation in IFN-gamma-knockout mice, indicating a critical mechanistic role for IFN-gamma.

CONCLUSION

This study demonstrates that IL-12 selectively inhibits BM eosinophilopoiesis, and that this effect is mediated by IFN-gamma. Intrapulmonary IL-12 has suppressive effects on BM eosinophilopoiesis that may represent a novel mechanism contributing to the anti-eosinophilic effects of IL-12 in allergic airway disease.